The inborn errors of metabolism that are currently under investigation are hyperlysinemia, Lesch-Nyhan disease, maple syrup urine disease and isovaleric acidemia. In all instances, studies are being conducted on the skin fibroblasts grown in tissue culture. Skin biopsies and blood samples (for lymphocyte culture) are obtained from the patients. Hair of patients with Menkes' kinky hair syndrome is being studied as an approach to the diagnosis.